The present invention relates generally to a brake system and method. More particularly, the present invention relates to a system configured to estimate a change in temperature of a brake component, a method of estimating the change in temperature of the brake component, and a system and method for applying a parking brake.
Standard braking systems for heavy vehicles, such as trucks, buses and coaches, include air actuated service brakes at each wheel of the vehicle including a membrane type brake chamber biased into a brake off condition, and brakes operable as service and parking brakes on some wheels (e.g., the rear wheels of a tractor unit of an articulated truck and trailer unit). Such combined brakes also include a membrane type air chamber. Behind that, a parking brake chamber is biased into a parking brake-on condition by a spring, but while the vehicle is in motion, is held in the off position by pressurized air introduced into the cylinder. To apply the parking brake, the air is vented, permitting the spring to extend and apply the brake. Such spring brakes maintain a high parking brake force even if the brake disc shrinks due to cooling.
It is desirable to replace the parking brake cylinder by an alternative apparatus of applying the parking brake that is more compact and reduces the amount of components in the vehicle's air supply system. To this end, the present applicant has proposed a number of alternative parking brake devices that utilize electromechanical components, such as electric motors, to apply the parking brake (see for example EP1596089 and EP1596090).
It has now been recognized by the present applicant that one problem with such parking brakes (and with standard spring parking brakes) is that they fully apply the parking brake at its maximum possible force, even if the particular conditions under which the vehicle is to be maintained stationary do not require such a high force to be used. This places the components of the brake, such as the caliper, the operating shaft and the pistons, under unnecessary stress, thus shortening the life of the brake. This problem is particularly acute for applications such as buses, where for instance the parking brake is automatically applied each time the passenger door is opened.
A further problem with known electromechanical parking brakes is that they may, under some circumstances, be unable to account for any shrinkage of brake components, primarily brake discs. Shrinkage may occur as such components cool while a vehicle is parked, following heating that has been frictionally induced by use of the service brake when the vehicle is in motion. If an insufficient parking brake force is maintained after cooling, there is a danger the vehicle may roll away. An additional problem is how to implement such an electromechanical system, including its control in a safe and low cost manner.
The present invention seeks to overcome, or at least mitigate, the problems of the prior art.